feat: LSP autocomplete module declaration

[asterite]

Description

Problem

No issue, just something that Rust Analyzer does but our current LSP doesn't.

Summary

Example for a "main" module:

Example for a "non-main" module:

Additional Context

Documentation

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Compilation Time'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 7e5b0f3	Previous: 02056d6	Ratio
rollup-merge	2.426 s	1.972 s	1.23

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench